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In last month's column I referenced some new technologies for mold cooling and the positive impact they will have on the pro- cess. But there is still plenty going on with current cooling methods and how they are being underutilized in many cases. For example, over the course of my career I have been part of many discus- sions about small cooling lines and bubblers and their tendency to plug up. This is something that you should not overlook in your water-treatment procedures. If your small water lines are plugging up, you obviously are having some sort of buildup in your other water lines too. This may not reduce your flow volume in gal/min (GPM), but will certainly have an impact on cooling and your ability to pull heat out of the plastic. So if buildup or plugging issues are a reason to not maximize your cooling and cycle times, you should focus on the root cause of the issue with the water treatment and not cut short your potential to reduce cycle times by exploring various cooling options. You always have to look at the big picture to understand the overall payback. In last month's column I also mentioned how important it is to consider the plastic material being used and to focus on cavity details that create steel conditions that will maintain heat, which contributes to quality issues and excessive cycle times. I stress this because the mold design cannot treat all materials the same with regard to cooling, steel/alloy selection, ejection, and lifter travel. How small can you go with water lines? There is some new technology that uses liquid CO2 in lines as small as 0.060 in. to Let's Get Serious About Mold Cooling get into tight areas. I have not used this technology, but I can see where it could have a big impact in some situations. But in most cases, with a bit of creativity, we have been able to add water where others have said it was not an option. Let me give you some details on one such project. On a small four-cavity tool, the part had a U-shaped notch in the center. The steel that cored out and created the notch was very thin— roughly 0.100 to 0.150 in. thick, 0.750 in. tall, and 0.750 in. wide. This steel section retained heat, not allowing the plastic to cool and requiring an excessively long cycle time of 40 sec. Any shorter cooling time would cause the hot plastic in the notch area to shrink smaller than the spec for the notch gap dimension. This steel was in the solid and adding water was not considered an option because the steel was so thin. A copper alloy material could have helped here, but to insert this area at such a late stage would have been very expensive. So we considered an option that most would have thrown out the window. We EDM hole-popped some 0.060-in. water lines with a circuit that looped through all four cavities. This was one of those cases where you really don't know what to expect until you try it. When we set the tool, water was just trickling out of the new line because it was so small. The results were amazing: This small amount of water flow through the thin steel had such a big cooling effect that even at a 17-sec cycle time (a 23-sec reduction) the notch gap on the parts were now too large! Our option was to run the small cooling line at a much higher water temperature to keep the part from cooling too quickly. Though we were greatly surprised by the effect, when consid- ering ratio of this "micro" water-line size to the steel thickness surrounding it, the water line was actually quite large. A 0.060-in. water line in a steel section 0.100-0.150 in. thick compares to using a 0.600-in. cooling line in a steel section 1-1.5 in. thick. Out of curiosity, we then ran compressed air instead of water through the micro cooling line. This also had a big impact on cooling With a little creativity, I have been able to add water where others said it was not an option. Some creative thinking with conventional technology, like small cooling lines and bubblers, can generate big improvements in cooling and cycle times. By Randy Kerkstra PART 2 Cross-section of a bubbler in a slide shows cavity detail with internal water loops for the In and Out water flows. 38 AUGUST 2016 Plastics Technology PTonline.com K now How TOOLING